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Dual Thermocouples On One Analog Pyrometer


Joseph

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I have an ACI Pyrometer kit. Is it possible to add a switch and hook a second thermocouple to the gauge? I realize the wire length is part of the calibration so I would get another with the same length and the switch will throw it off a hair. Perhaps there would be a way to compensate for this by changing the resistor on the back? thanks for the advice.

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If you don't use a compensated switch you will experience some problems.  Unfortunately the switch costs more than what you now have.  A dual input Digital type K HH308 costs $99 from Omega but you need to adapt to a mini connector to the thermocouple.  There are also some type K plugs and jacks that are compensated that will work.

David

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If you want any accuracy  or repeatability you need to realize a regular switch is going to give you all kinds of weird readings, drift with temperature changes etc., this is because every connection is different material and will in turn act as a thermocouple.  A reasonable way to keep the accuracy of what you now have is to put a thermocouple recptacle on of near the panel meter and t/c plugs on the thermocouple extension wire and plug the T/C you want to read into the T/C receptacle.  Look on www.omega.com  search for part number RSJ which is a panel receptacle from $2.45 to $5.00, search for part number OSTW-CC-K-M which is a plug $2.95.  If you don't care just put in a cheap switch.

David

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Thermocouple voltages are created by the temperature gradient along the thermocouple (and wire), not the junction. As long as there is no temperature change across the junction (switch, terminal, etc), the reading will not be affected. The terminals on a toggle switch are so close together that there's no temperature difference. This is why the terminals on a typical ceramic thermocouple block used by most (all?) kiln manufacturers are simply brass terminals with steel screws.

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